In general, a radiographic imaging apparatus that utilizes a function of radiation passing through substances is used widely for medical image diagnosis and for non-destructive examination. For the radiographic imaging apparatus used for mammography, in particular, there has been usually conducted a method to radiograph by fixing a subject on a subject table that is integrated with a radiation image detector. However, in this method, there have been problems that image contrast is not enhanced sufficiently and image sharpness is insufficient as a medical imaging apparatus used to make out microscopic structure of a specific region such as a pathological portion of a breast, although a subject can be radiographed on the exact size.
In recent years, therefore, there has been proposed a radiographic imaging apparatus that radiographs a phase contrast image. The phase contrast image is one which is also called a refraction contrast image, and is one which was earlier said to be obtained by radiographing with monochromatic parallel radiation obtained from radiation source such as SPring-8 or by radiographing with a micro-focus radiation source having a focus size of about 10 (μm). However, it has been found that the phase contrast image can be obtained even by a radiation source (small focus radiation source having focus size 30-300 (μm)) used in general medical facilities.
For example, in Patent Document 1, there is described a technology to obtain an effect of edge enhancement without using a synchrotron radiation light that requires a large-sized apparatus and without using a small-sized X-ray light source having an X-ray focus size that can be regarded as a point source of light. This Patent Document 1 shows that, when X-ray focus size D is 30 (μm) or more, distance R1 covering from an X-ray tube representing a radiation source to a subject represents an area satisfying an expression of R1≧(D−7)/200 (m), and when distance R2 is 0.15 (m) or more, an edge enhanced image can be obtained. In this case, the radiographing is enlarging one with an enlargement factor that is expressed by (R1+R2)/R1.
In the past, incidentally, when changing an enlargement factor in a radiographic imaging apparatus that conducts phase contrast radiographing, the aforesaid R1 is fixed and R2 is changed to change the enlargement factor as is shown in Patent Document 2, for example.
Patent Document 1: Unexamined Japanese Patent Application Publication No. 2001-91479
Patent Document 2: Unexamined Japanese Patent Application Publication No. 2004-173879